It is quite common for the playing surface of a pool table to require leveling. This need can arise because the floor on which the table sits is not level, or because the table itself is not level, or both. Numerous attempts have been made to provide solutions to this leveling problem.
Perhaps the most common and well-known solution is leveling the table by placing shims under the feet of one or more of the table's support legs. The shims may often simply be folded pieces of paper, match book covers, or even slivers of wood. Some shims are even sold at retail, with hard rubber disks being popular, for example. As leveling solutions, shims are simple and somewhat effective, but are generally lacking in durability and ease of use.
Another simple solution is through the use of a leveling foot, a device which is often used on chairs, tables, and other furniture to extend their legs. The leveling foot includes a threaded shaft having a larger diameter circular foot on its lower end, and with its upper end extending into a threaded sleeve in the leg of a table, for example. By turning the foot in the desired direction, the shaft may be caused to extend from or retreat into the leg. In this way, the leg may be made effectively longer or shorter, thereby raising or lowering the table as desired. While this is an effective approach for some furniture, it is less effective for pool tables. For one thing, it requires that the leveling foot be un-weighted while the foot of the device is rotated. This works best with lighter furniture such as chairs or light tables. However, pool tables often weigh several hundred to a thousand pounds or more, which would make un-weighting the leveling foot awkward at best. In addition, a leveling foot would be quite difficult for the average user to retrofit to a pool table, further limiting its usefulness.
A basic leveling foot arrangement is depicted in U.S. Pat. No. 7,654,911 B2 to Cartwright. Cartwright uses an internally-threaded insert 24, which includes a threaded metal sleeve with a flange 25 at one end. A hole must be drilled in the bottom of the table leg to allow the insert to be placed in the leg. This allows the rod 22 of leveling foot 26 to be inserted into sleeve 30, with the entire combination being fitted into the furniture leg 14. Knob 28 is provided to allow the leveling foot to be operated while the device is still weighted. However, the knob of Cartwright is better suited for use with lighter furniture, as turning the knob while supporting the large weight of a pool table would be difficult.
A variation of the leveling foot approach is shown in U.S. Pat. No. 6,729,590 B2 to Gabriel. The device of Gabriel is designed such that it could be operated while still supporting the weight of a pool table. This capability is accomplished by providing a worm gear for driving a driven gear, which in turn drives an elevation shaft to raise or lower an object. However, operating the Gabriel device while still supporting the weight of a heavy pool table would cause large amounts of friction between the threads of the worm gear and those of the driven gear. This degree of friction would require a relatively large amount of force to overcome, and would also necessitate that the device be constructed of steel or other hard metal.
Other variations of the leveling foot approach are disclosed in U.S. Pat. No. 1,417,639 to Sterner; and U.S. Pat. No. 3,653,341 to Nielsen. Each of those devices provides a way to drive the leveling foot while still supporting the weight of the table. However, all of the leveling foot devices suffer from friction problems similar to those found with Gabriel. In addition, none of the devices, including Gabriel, are suitable for retrofitting to an existing pool table having no leveling capabilities. Therefore, the devices must be included in the legs of a table when it is sold, which may be seen as an unnecessary added expense by potential buyers of the table. In addition, home pool table legs are often thin at the bottom, making them further unsuited for enclosing a leveling foot device.
The friction problems associated with the Gabriel, Sterner, Nielsen, and Cartwright devices could be overcome by utilizing an arrangement of balls or rollers traveling in lifting ramps or grooves between two surfaces as may be seen in U.S. Pat. No. 7,878,543 B2 to Bodtker et al.; U.S. Pat. No. 7,252,017 to Kramer; and U.S. Pat. No. 5,106,349 to Botterill et al. In each of the foregoing patents, two opposing plates or disks have lifting ramps in which balls travel when one of the plates is rotated. As the balls rise or sink on the lifting ramps, an axial motion is created, which may be used to raise or lower a supported object such as a pool table.
However, in order to raise or lower a pool table, at least three plates would be required. This is due to the fact that the upper and lower plates would necessarily be non-rotatable while the device was bearing the weight of the table. Yet the aforementioned patents disclose devices with only two plates having opposing grooves in which balls would travel. Therefore, it is necessary to provide some means for handling the friction between the surfaces of the two plates having no opposing grooves between them. One way to handle this friction is disclosed in U.S. Pat. No. 8,662,260 B2 to Baldeosingh et al., which uses a thrust bearing to reduce friction. U.S. Pat. No. 4,016,957 to Osujo et al. uses Teflon for a wear surface, while U.S. Pat. No. 7,735,612 Pozivilko et al. uses a Boss washer and a retaining washer as a bearing surface.
While all of these solutions are effective in handling friction between plates, they each require additional parts or material which does not contribute directly to the lifting function of the device. In addition, having two plate surfaces with no grooves therein makes the device unnecessarily thicker, for a given amount of lift. This is counter-productive, since it is of critical importance that the height of the device be kept as low as possible, while still producing sufficient lift. A low height is necessary for any device which is to be retrofitted to the foot of an existing pool table leg, as the overall height of the pool table cannot be excessively increased without changing the look and feel of the game to the players, which would make the device unacceptable. It is thus critical for a retrofittable leveling device to seek the most lift with the least height possible. This is especially true since the weight of a pool table may exceed a thousand pounds.
Some of the foregoing problems are alleviated by U.S. Pat. No. 5,713,446 to Organek et al; and U.S. Pat. No. 5,078,249 to Botterill. The devices of Organek and Botterill provide three plates, with 2 sets of balls traveling in two sets of opposing grooves. In this configuration, the friction between the second set of opposing surfaces is handled by the second set of balls themselves, without the need for additional parts merely to handle the friction. The second set of balls also provides a lifting action, thereby making more effective use of the height of the device to produce lift.
However, the configuration of Organek and Botterill results in essentially maximizing the required thickness of the control plate, and thereby unnecessarily increases the overall height of the device for any given lift provided. This unwanted result occurs because both devices “stack” the grooves on the upper surface of the control plate directly over the grooves on the lower surface of the control plate, bunk bed style. In particular, the deep end of each lower groove is directly underneath the deep end of a respective upper groove. This means that the thickness of the control plate must be equal to twice the deepest depth of a groove, plus a minimum material thickness between two grooves. This would not work well for a retrofittable leveling device for a pool table, to be placed under one or more legs of the table. Such a retrofittable device would necessarily be capable of generating the required lift, without being so thick as to disturb the look and feel of the game by adding excessive height to the playing surface of the table.
There is thus a need for a leveling device which is capable of producing sufficient force to raise and lower a pool table of substantial weight. The device would be retrofittable to an existing pool table, without a need for the owner to perform complex tasks, such as drilling a hole in a pool table leg in order to insert components of the device. The use of the leveling device should also not disturb the aesthetics of the table itself. When installed under a leg of the table, the thickness of the device would ideally add as little to the height of the table as possible, while still maintaining the capability to raise and lower the table easily.